Luminescent tube and system



Feb. 13, 1940. c. P. BOUCHER LUMINESCENT TUBE AND SYSTEM Filed May 22, 19s? '2" Sheets-Shet 1 c'w-zes 12 B0 Feb. E3, 1940. c. P. BOUCHER 2,190,009

LUMINESCENT TUBE AND SYSTEM Filed May 22, 1937 2 Sheets-Sheet 2 3m CfiarZeaPBoacker my /ww Patented Feb. 13, 1940 UNITED STATES LUIVIINESCENT TUBE AND SYSTEM Charles Philippe Boucher, Montreal, Quebec,

Canada, assignor to Boucherlnventions, Limited, a corporation of Delaware Application May 22, 1937, Serial No. 144,285

7 Claims.

My invention relates to luminescent tube systems and apparatus, and more particularly concerns high voltage luminescent tube systems and apparatus for the emission of light of a selected composite quality and color.

One of the objects of my invention, therefore, is the production of a simple, economical and dependable luminescent tube system and apparatus for the production of a composite beam of light of selected quality and color, characterized by the substantial absence of fringing, i. e. the production of the colors of the spectrum where the component beams merge'and blend with each other to produce the final, composite i5 beam.

Another object is the production of a luminescent tube system of the character described which is peculiarly adapted to give brilliant, efficient and uniform operation over long periods of use with a minimum of attention and/or repair.

Still another object is the production of high voltage luminescent tube systems and apparatus for the production of a composite beam of light of selected quality and color, in which condensive effects and other electrical break down phenomena are reduced to a minimum and which are well adapted to withstand the many varying conditions encountered in actual practical use. Other objects will be apparent in part, and in part pointed out hereinafter.

The invention accordingly consists in the combination of elements, features of construction and arrangement of parts as described herein, the

3-3 scope of the application of which is indicated in thefollowing claims.

In the accompanying drawings:

Figure 1 represents a luminescent tube system and apparatus in accordance with my invention,

10 certain parts being broken away to more clearly disclose other parts and certain parts being illustrated diagrammatically,

Figure 2 is a cross-sectional view, on an enlarged scale, of certain portions of the apparatus =3 as seen at the line 2--2 of Figure 1 looking in the direction of the arrows,

Figures 3 and 4 respectively represent longitudinal and cross-sections of a modified luminescent tube construction, and

5-.) Figure 5 represents a luminescent tube system which is a modification of the system shown in Figure 1.

Like reference characters denote like parts throughout the several views of the drawings.

:- As conducive to a clearer understanding of certain features of my invention, it is to be noted at this point that although luminescent tube systems and apparatus have come into widespread use in the display and industrial arts, as witness the familiar orange-red neon signs or displays of stores and theatres, and the blue mercury-arc lamps used in printing industries and the like, the art has so far been limited, from a practical standpoint, to a few basic or fundamental colors. These are the characteristic radiations of the elemental gases when energized. In display work a variety of colors is often desirable from a standpoint of novelty and appeal to the eye. In the industrial arts, however, little has been accomplished in obtaining a true white light, withits absence of detrimental shadow, and its ease on the eyes. In this the art has progressed but little since its pioneer days, despite the considerable research activity along those lines. 20

While it has been recognized that, along the lines of conventional teachings of physics, it is theoretically possible and perfectly feasible to compound the radiation from a plurality of luminescent tube sources to produce the desired 95 composite light, as a practical matter but little of a commercially feasible nature has been proposed. In short, the art of compounding radiation from a plurality of luminescent tubes, each of a different color characteristic, has been at a 39 practical standstill. In all such composition of radiation, as for example, in the production of light approximating the quality of sunlight, it is necessary to place the tubes, each capable of producing a ll light of characteristic color, in a side by side relationship and as close together as possible, in order to facilitate the light blending, as well as to minimize the over all dimensions of the assemblage, for economic and aesthetic purposes. 40 When comparatively low operating voltages are used, the spacing between the tubes can be quite small, even almost infinitesimal, so that the quality of the light resulting, considered apart from the aspects of production, is reasonably satisfactory. It is apparent, however, that when low voltages are employed, the lengths of the tubes become quite limited. Instead of being able to use the comparatively economical long tube, a plurality of short tubes must be used. This increases the cost of installation. In addition, the use of short lengths of gaseous discharge tubing always is not possible because of structural limitations in the luminescent dis-- p y- 88 An object of my invention, therefore, is to eliminate the foregoing disadvantages, and in so H doing, to cheapen the installation and operating costs, as well as to carry out the proper blending 4 into display signs, and more economical to opcrate per unit of emission. Here, however, the efforts of the investigators have met with but little practical success. Ordinary elongated tubes of the art were employed. Because of the high voltages at which the tubes were operated, the investigators found that if the tubes were placed close together side by side, as is essential for completely satisfactory blending, then because of the difference of potential existing between adjacent portions of the tube, condensive action occurred, the resulting strains frequently resulting in a rupture of the walls of the tubes.

To prevent this disruptive and disastrous condensive action, the tubes were separated a safe distance. Unfortunately, under these conditions of operation, poor blending of the light rays resulted, as well as unsatisfactory distribution of illumination. Considerable fringing around the shadows occurs, i. e. the fundamental blue, red, yellow colors of the spectrum, as well as green, are found around the shadows produced by modern tube lighting. These drawbacks make such sources of blended light unsuitable for many important purposes, such as motion picture studios, projecting beams and the like in industrial and home illumination. Furthermore, this necessity of spacing apart the component tubes materially increases the costs of a given installation.

An object of my invention, therefore, is substantially to eliminate the difilculties encountered hitherto in the use of high voltage gaseous discharge tubes in the production of composite radiation, and also to operate comparatively great lengths of luminescent gaseous discharge tubing for such purpose without the harmful condensive effects heretofore encountered.

Referring now more particularly to the practice of my invention, attention is directed to Figure 1 of the drawings wherein luminescent tube apparatus generally indicated at I is energized by high potential electrical transformer apparatus I I supplied with alternating current electrical energy at, say, 60 cycles, 110 volts, by source of supply l2.

Luminescent tube apparatus I0 (see also Figure 2) consists of an elongated gaseous discharge tube 13 having a collapsed wall portion l3a into which is fitted a second elongated gaseous discharge tube I 4.

The tube I3 illustratively contains a gas such as neon at a very low pressure. In order that its walls may withstand the atmospheric pressure exerted on them and, further, in order that a fairly uniform luminescence be preserved throughout a broad field of vision, the tube is substantially crescent-shaped in cross-section (see Figure 2). The curvature of the inner or concave portion I311 conforms to that of the second luminescent tube I4 in order that good contact with a minimum spacing be preserved between the tubes. The curvature of the outer wall I3b of tube I3 is regular and assures a gradual the said bosses.

and uniform change in the gas space of the tube in progressing from a center part of the tube in either direction. At the edges I30 and 13d of the tube, the curvature is such as to give a sufliciently narrow gas-space and yet permit adequate strength at these points.

Tubes I3 and I4 are maintained in proper contact relationship by means of suitable spring clips I5. Preferably these clips are fashioned of non-magnetic stainless steel. The clips hold the tubes I3 and I4 in loosely interfitting relation, so that the tubes are free to slide longitudinally relative to each other. Stainless steel clips have the further advantage of serving as a reflector which is always clear and has high reflecting properties for light emitted by the tubes. Because of the non-magnetic character of the clips I5 no magnetic pull is exerted on the conductive column of gas in the tubes and operation of the tubes is, therefore, unaffected thereby.

Good results are obtained when the metal is applied in sections along the lengths of the tubes, as in Figure 1, spaced apart a convenient distance, say roughly to Such spacing is sumcient to avoid any harmful condenser action between any two widely spaced points along the length of the same tube. These reflector clips may be made as long as six inches without detrimental condensive action.

Absolute freedom of the tubes to slide relatively to each other is essential, especially when the two tubes are fashioned of different glasses. To the end of securing the tubes together by means of the reflecting clips I5 in order-to assure complete freedom of longitudinal motion, I conveniently strike up bosses or ridges I3e along the outer sides of tube (see Figure 2) These appear near the region where the reentrant wall l3) starts. The ends I511 of clips I5 are shown as inwardly curved so as to snap downwardly and over By tension, clips I5 are firmly secured against the tube I3. The compressive action of the middle part I5b of clip I5, as seen in Figure 2, insures that tube I4 is forced firmly against the tube l3.

A further function of clips I5 is to provide a reflector for the light emitted by luminescent tubes I3 and I4. Where desired, however, tubes I3 and Il may be secured together in any suitable manner and reflector means provided, such as metal foil secured to the tube by insulating varnish. Likewise, some molded composition having an inner surface coated with a desired reflecting substance is satisfactory. In this construction both the molded composition as well as the surface coating are electrical insulators in order to assure a freedom from disturbing the potential gradients along the tubes as a result of the applied operating potentials.

Luminescent tube I4 illustratively contains a mixture of gases, such as neon and mercury vapor, at a desired pressure. Preferably the sectional area of tube I 4 is such as to give a high current density and emit intense visible radiation. Conveniently, this tube is designated as the light emitting tube. The tube I3, in comparison, is preferably of such sectional area as to employ a comparatively low current density. The light emitted from this tube is just suflicient in color and intensity as to supply any deficiency coming from the light emitting tube I4. Consequently,

" this tube I4 is designated asthe blending tube.

Both tubes, however, are preferably of like ourrent-energizing capacity as well as striking potential, for reasons as appear more fully hereinafter.

Because of the relatively high current densities to be used in the operation of gaseous discharge tube I4, this tube is of smaller area than tube I3.

The blending tube I3 may be of comparatively slight luminosity as desired.

In the production of white light, for example, the tube I4 may consist of magnesia glass colored very slightly yellow and known to the trade as canary tubing. It is filled with neon gas to which is added mercury. Upon energization of this gaseous discharge device a light green light is emitted. This light, of course, is in the form of a soft glow characteristic of gaseous discharge tubes, the green color resulting from a filtration of the violet light of mercury vapor through the yellow glass walls of the canary tubing. The crescent-sectioned blending tube I3 may be as nearly colorless and transparent as possible. For this purpose the tube I3 may be made of soda glass tubing containing neon at low pressure. Energization of this tube, in a manner more particularly described hereinafter, produces a dull orange glow so characteristic of neon.

Because of the relative positioning of the lightemitting tube I4 and the blending tube I3, the orange-red characteristic radiation of tube I3 combines with and supplements the greater volume of pale green light coming from tube I4. This effect is greatly aided by the reflector clips I5 spaced along the lengths of tubes I3 and I4 and securing these tubes together. By this blending and filtration there is produced the desired composite white radiation. It will be understood that where desired either one of the gaseous discharge tubes may consist of a mixture of inert gases giving off desired light in matters of color and intensity to achieve the required composite result.

Since blending tube I3 is preferably operated at comparatively low current densities, it can be formed of soda glass. This glass tubing is satisfactory for densities of say 25-60 milli-amperes, without undue overheating. On the other hand, since tube I4 is preferably operated at high current densities, hard glass such as Pyrex or Onyx or like magnesia glass is employed. The magnesia glass tubing is advantageously employed, despite its comparatively high cost, for current densities in excess of 60 milli-amperes.

In order that eflicient illumination may be achieved at a minimum expense of installation, operation and maintenance, tubes I3 and I4 are comparatively long. Of necessity they are operated at high voltages, that is, on the order of some 5,000 to 15,000 volts or more. As pointed out hereinbefore, difficulty has previously been encountered in successfully operating parallel gaseous discharge tubes at such voltages. For satisfactory results, these tubes I3 and I4 are disposed in mechanically parallel relationship, that is, side by side, and closely adjacent each other. Where they are spaced apart any appreciable distance, fringing or breaking up of the light into the primary and secondary spectral colors takes place at the shadows. Furthermore, poor blending of the component light beams and directional transmission of the composite beam also results. Certain objections are encountered in this construction as indicated above in discussing certain practices of the prior art. Thus, when the gaseous discharge tubes are placed adjacent to each other, and high voltages are then impressed across the terminals of the tubes, thegas columns present in the tubes are good conductors. The glass walls of the tubes serve as the dielectrics. A condenser is formed thereby which may be of such capacity, which with the inductance of the transformer secondary winding, gives rise to electrical oscillation producing exceedingly high peak voltages. These voltages may puncture the insulation of the coils of the secondary windings. Furthermore, the high voltage strains produced at contiguous points. along the lengths of the tubes may be suiiicient to rupture the tube walls.

In accordance with the provisions of my invention, I avoid the aforementioned difflculties in an ingenious manner. Thus, considering Figure l of the'drawings, it is to be noted that the tubes I3 and I4 are of substantially the same length. It will be observed that the discharge space is substantially the same for both tubes. The relative gas pressures are such that the resistivity per unit of length of the tubes also is approximately equal. To this end, and since the tube I3 is of a crescent-cross-section throughout the great part of its length must be of substantially full circular cross-section in the region of the electrodes, I find it desirable to bend the ends I4a and Nb of tube I 4 upwardly, out of the plane of the tube I3. In this manner the interelectrode space in tubes I3 and I4 is substantially the same.

This equality of length for the two tubes alone is not sufficient. While the potential drop along the length of each tube is equal in both cases, giving equal potential gradients along the lengths of the tubes, nevertheless if the current flow in the two tubes is in opposite directions the voltage difierence'between any two points contiguous to each other along the lengths of the tubes will be approximately the full voltage impressed across the terminals of the tube. Such a potential difference would result in a rupture of the tube walls. The controlling requirement is that the voltage and directional gradients in the two tubes be substantially equal. One element of this definition is satisfied by making the tubes of'equal length. The other is satisfied by impressing voltages of equal values and of like phase across corresponding terminals of the tubes.

Accordingly, in the practice of my invention, I employ a transformer having a single primary winding and two secondary windings. As schematically illustrated in Figure 1 of the drawings, this transformer generally indicated at I I has a primary winding I6 supplied from a suitable single-phase source of alternating current electrical energy I2 by way of conductors I1 and I8. Transformer II also includes two secondary windings I9 and 20, each comprising two coil sections, I9a and I9b for winding I9 and 20a and 20b for winding 20. The coil sections of each winding are wound in the same direction and are connected together in series aiding relationship. The midpoints of the two secondary windings I9 and 20 are grounded as at ZI and 22 respectively. In this way the voltage of the terminals of the secondary windings with respect to ground amounts to only half the potential difference between pairs of terminals. Primary winding I6 is electromagnetically linked with secondary windings I9 and 20 by Way of an iron core generally indicated at 23. Preferably the core construction is such as to permit a high leakage reactance of the transformer under load condltions.

Now in order that the individual luminescent tubes I3 and I4 comprising the luminescent display Ill be subject to like potential gradients at contiguous points along their lengths, corre- 15 spending terminals of the tubes are connected to corresponding terminals of the two secondary windings. Thus, corresponding terminals I37: and llh of tubes l3 and H are connected by way of conductors 24 and 25 to corresponding terminals 20c and l9c of transformer secondary windings 20 and I9 respectively. Likewise, corresponding tube terminals I37 and I47 are connected by conductors 26 and 21 to corresponding secondary winding terminals 20d and I912. By this construction, for an assumed point in the cycle of operation where the current, acting under an induced electromotlve force in secondary winding 20 in a downwardly direction as seen the drawings, flows from winding 20 by way of terminal 200, conductor 24, gaseous discharge tube l3, conductor 23 back to winding 20 to complete the circuit. A similar flow of current takes place in tube H. In connection with the energization of this luminescent tube the current, acting under a corresponding electromotive force induced in winding 19, flows from winding l9 by way of terminal l9c, conductor 25, tube It, conductor 21, returning through winding terminal l9d to complete the circuit. For the assumed period in the cycle of operation the flow of current in tubes l3 and H is from left to right as seen in the drawings.

Because of the substantial identity of the electromotive forces induced in secondary windings 20 and I9 and the equivalency of the lengths of tubes l3 and I4, as well as their striking voltages and operating currents, the potential drops along both tubes are substantially the same. This identity in potential drop with length, or voltage gradient, assures a freedom from voltage differences sufficient to rupture the walls of the gas-' eous discharge tubes. In addition, this equivalency of potential gradient at various contiguous points along the lengths of the tubes precludes condensive effects between tubes, thereby preventing the establishment of oscillating conditions and the arising of electrical potentials destructive to the transformer secondary windings.

In the operation of my luminescent tube system and apparatus a balanced condition of operation is assured at all times by virtue of like transformer secondary windings and the grounding of each of these windings at its midpoint. While corresponding terminals l3h and Nb of tubes (3 and N are at, for example, maximum positivepotential with respect to ground, the corresponding terminals I37 and My will be at maximum negative potential. Similarly, when tube terminals I37 and My are at maximum positive potential with respect to ground tube terminals l3h and Mn will be at maximum negative potential. Symmetry, therefore, is always preserved in the operation of the system.

By my novel luminescent tube system and apparatus, light emission of from 45 to lumens per watt input of electrical energy is obtained as contrasted with the ordinary incandescent lamp of l2-to 15 lumens per watt input.

While in the illustrative embodiment of my invention discussed above parallel nested luminescent tubes are employed, certain advantages and economies are realized by employing a luminescent display comprising parallel gaseous discharge tubes, one mounted within another.

Thus, referring to Figures 3 and 4 of the drawings the tube 30, similar in purpose to tube l3 of Figures 1 and 2, is substantially circular in section. Since this tube ordinarily serves. as the blending tube, and hence usually operates at comparatively low current densities, tube 30 conveniently is fashioned of soda glass just as in the case of tube l3. The tube 3|, which is similar to the tube ll of the embodiment indicated in Figures 1 and 2, is disposed entirely within the tube 30.

The two tubes 30 and 3] are sealed together in any suitable manner. Conveniently, the inner tube Si is maintained in desired position in tube 30 by means of the incoming terminal member 32. This terminal member is preferably fashioned of a heat-resisting conducting material, such as non-magnetic sta nless steel, which possesses sumcient strength at the high tempera tures reached in the tube to maintain the inner tube 3i in proper position and yet which yields sufliciently to accommodate the difference in expansion between .tubes 30 and 3|. Since tube 3| is run at comparatively high current densities. this tube is preferably formed of heat-resistant glass, such as Pyrex or the like.

In order to enjoy maximum benefit in the operation of the luminescent display disclosed in Figures 3 and 4, reflectors 33 are spaced along the length of tube 3!]. Tube 3! is disposed eccentrically within the tube 30, so that it lies closely adjacent the reflectors 33. The desirability of this eccentricity is dictated by the fact that illuminated displays usually face in one direction only. The radiation, therefore, is thrown in that direction. The eccentricity of the positioning of tube 3| within tube 30 is further necessitated by a desire to achieve a proper blending and diffused reflection of the light emitted by the two tubes. When tube 3| is-disposed centrally of tube 30, unsatisfactory reflection results, and improper blending occurs, resulting in detrimental and undesirable fringing in the shadows.

The construction of my luminescent tube display in accordance with the embodiment shown in Figures 3 and 4 possesses the material ad-- vantage that the direct radiation from the principal source passes through only two giass walls (its own and one wall of tube 30) on its journey to the exterior. In the case of the embodiment illustrated in Figures 1 and 2, the radiation must pass through one wall of tube l4 and both walls of tube l3, resulting in somewhat higher refraction of rays and more absorption. As a result the arrangement indicated in Figures 3 and 4 is more emcient than that of Figures 1 and 2.

There is the further advantage, in connection with the embodiment of Figures 3 and 4, in that the assembly is neater and more compact. The spring action of clip reflectors 33, where these reflector elements are formed of spring clips, serves no other purpose than to secure the clips to the tube 30. The clips no longer are relied upon to hold the two tubes together.

While in the embodiment of my invention, as illustratively described above in connection with Figures 1 and '2, more specifically relates to the operation of a luminescent display comprising two tubes by means of electrical transformer apparatus having two secondary windings, certain advantages are realized where two luminescent displays are operated from a single transformer of the double type, that is, having two secondary windings. Thus, turning to Figure 5 of the drawings, the two luminescent displays 40 and 4| are supplied with alternating current electrical energy at ;'8. desired high potential by double transformer 42.

Displays, and ll are shown as comprising small tubes 42 and 43, respectively, nested in the crescent-shaped recesses of the corresponding larger tubes 44 and 45. All tubes are of substantially the same length in order to achieve a uniform distribution of potential throughout the lengths of the tubes. The two tubes comprising each display are secured together in any suitable manner. Sufficient freedom of motion is permitted, however, to accommodate the difference in longitudinal expansion of associated tubes.

The two luminescent displays 40 and 4| are supplied with high potential alternating current electrical energy from the two secondary windings 46 and 41 of transformer 42 diagrammatically illustrated as interlinking primary winding 48 through an iron core generally designated as 49. Alternating current electrical energy, for example, single phase 60 cycle, 110 volts, coming from the source of supply 50, serves to excite primary winding 48.

In this double transformer illustrated in Figure 5 each secondary winding 46 and 41 respectively consists of two coil sections 46a and 46b and 41a and 4111 connected in opposed phase relationship, that is, with the induced electromotive forces bucking each other and preventing a flow of current from one coil section into the related coil section.

Energization of tubes 43 and 45 comprising display 4| is effected from the respective coil sections 46b and 41b of secondary windings 46 and 41. Alternating current electrical energy for coil section 46b is supplied tube 43 by way of conductor 5| and returns through conductors 52, 53 and ground 54. It is to be particularly noted that potentials corresponding in direction and intensity are impressed across the terminals of tubes of display 4|. Therefore, the potential gradients at corresponding points along the tubes 43 and 45 are identical and freedom from condensive effects and high voltage rupture of the tube walls is thus assured.

Similarly, tubes 42 and 44 of display 40 are respectively energized by coil sections 41a and 460 by way of conductor 51, tube 42, conductors 58 and 53, and ground 54 (for the tube 42) and by way of conductor 59, tube 44, conductors 60 and 53, and ground 54 for tube 44. Here again like potentials are applied to corresponding terminals of the associated tubes of the luminescent display. Condensive eifects and otherwise disturbing effects are thus prevented.

Because of the symmetrical relationship between the two luminescent display apparatus and the energizing transformer apparatus of like symmetry, balanced operation with corresponding high efliciency and freedom from disturbing high potential transient effects is achieved. In this embodiment of my invention, however, it will be understood that for a maximum operating potential to ground equal to that of the embodiment more particularly described with reference to Figure 1, the luminescent tubes are only of one-half the length and voltage rating although the same current rating may be preserved.

Thus it will be seen that there has been provided in this invention a luminescent tube system and apparatus in which the various objects hereinbefore noted, together with many practical advantages, are successfully achieved. It will be seen that the apparatus is simple, compact, efficient and thoroughly reliable, and furthermore, that it is well adapted to give desired intense illumination of a desired color or combination of colors. While as illustrative of the practice of my invention the blending of illumination from two gaseous discharge tubes is discussed, it will be understood that, where desired, light from three, four or even more luminescent tubes may be composed, it being necessary, however, that the luminescent tubes be maintained in intimate parallel association and that they be energized from sources of like potential maintained in synchronism as by using a three, four or more secondary winding transformer of proper symmetry.

Since many possible embodiments may be made of my invention and since many changes may be made in the embodiments hereinbefore set forth, it will be understood that all matter described herein, or shown in the drawings, is to be interpreted as illustrative, and not in a limiting sense.

I claim:

1. In luminescent tube apparatus of the character described, in combination, a. luminescent tube, a second luminescent tube, and non-magnetic reflector means engaging and maintaining said tubes in parallel relationship permitting relative longitudinal motion of said tubes.

2. In luminescent tube apparatus of the character described, in combination, a luminescent tube, a second luminescent tube, and non-magnetic stainless steel spring clips maintaining said tubes in parallel relationship permitting relative motion therebetween and also serving as a reflector for the light emitted from said tubes.

3. In luminescent tube apparatus of the character described, in combination, a luminescent tube of a generally crescent-shaped cross-section, a second luminescent tube, and non-magnetic reflector means for maintaining said tubes in parallel relationship with the second-mentioned tube interfitting the concavity of said first-mentioned tube and permitting relative longitudinal motion therebetween.

4. In luminescent tube apparatus of the character described, in combination, a luminescent tube of generally crescent shape in cross-section containing a gas or mixture of gases, a luminescent tube of generally circular section containing a difierent gas or mixture of gases, and means for maintaining said tubes in parallel relationship with the second-mentioned tube interfitting the concavity of said first-mentioned tube and permitting relative longitudinal motion between said tubes.

5. In luminescent tube apparatus of the character described, in combination, a luminescent tube having walls of soda glass containing a gas or mixture of gases, a second tube of substantially lesser sectional area and having walls of Pyrex glass containing a different gas or mixture of gases, and means for maintaining said tubes in linear relationship permitting relative motion between tubes, whereby there is achieved a compounding and blending of light emitted from said tube.

6. In luminescent tube apparatus of the character described, in combination, a luminescent tube having walls of soda glass and containing a gas or mixture of gases, a second tube of lesser sectional area containing a different gas or mixture of gases and having walls of Pyrex glass, and reflector means positioned to reflect light from said tube of lesser sectional area through said other tube of greater sectional area and for maintaining said tubes in parallel relationship with relative longitudinal motion therebetween.

'7. In lurninescent tube apparatus of the character descbibed, in combination, a luminescent tube having walls of soda glass of generally crescent. shape in crosssection containing a gas or mixture of gases, a luminescent tube having walls of magnesia glass of generally circular section containing a different gas or mixture of gases, and means for maintaining said tubes in parallel relationship with the second-mentioned tube interfitting the concavity of said first-mentioned tube and permitting relative longitudinal motion between said tubes whereby there is achieved a compounding and blending of light emitted from said tubes.

CHARLES PHILIPPE BOUCHER. 

